OLED Covering Layer Uneven Surface Light Extraction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The low light output efficiency of OLEDs is due to total reflection phenomena caused by refractive index differences between the organic layer and the glass substrate, resulting in light being trapped and unable to emit into the air.
Innovation Solution
An OLED structure with a covering layer having an uneven surface, composed of layers with refractive index differences less than 0.1, such as a polycrystalline organic layer or small-molecular organic layers with specific glass transition temperatures, is used to reduce total reflection and enhance light emission efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional OLED structure with flat layers is used, then the fabrication process is simple, but the light output efficiency is low due to total reflection and waveguide phenomenon
Solution Approach 1:
The patent applies curvature by forming an uneven surface on the covering layer through crystallization processes. The surface transitions from flat to curved/uneven, which alters light refraction angles and reduces waveguide-mode light, thereby improving light output efficiency while maintaining fabrication simplicity
Solution Approach 2:
The patent changes the surface topology parameter of the covering layer from flat to uneven by controlling crystallization conditions. This parameter change modifies light propagation characteristics, reducing total reflection and enhancing light extraction efficiency without complicating the overall fabrication process
2Productivity
If the covering layer is made with materials having small refractive index difference (less than 0.1), then total reflection is reduced, but material selection and layer structure become more complex
Solution Approach 1:
The patent applies local quality by creating an uneven surface structure in the covering layer through selective crystallization. This local structural modification (uneven surface) is achieved in specific regions or layers without changing the entire device structure, thereby improving light emission while maintaining overall structural simplicity
Solution Approach 2:
The patent employs composite material structures by combining organic functional layers with covering layers of specific materials (e.g., TPBi, TCTA) that have appropriate refractive index differences. The composite structure of multiple organic layers with controlled crystallization properties achieves both improved light emission and manageable complexity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The uneven covering layer alters the refraction angle of emitted light, reducing waveguide-mode light and improving output efficiency, allowing more light to be emitted into the air, and the micro-cavity effect further enhances light output.
Implementation Method 1
A surface of the covering layer away from the base substrate is uneven... The uneven covering layer alters the refraction angle of emitted light
Implementation Method 2
a total reflection phenomenon will occur when light is emitted from a light-emitting layer formed of the organic layer to the glass and the air, i.e., light is enclosed between the organic layer and the glass substrate due to a waveguide phenomenon
Implementation Method 3
the uneven upper surface of the third small-molecular organic layer is obtained by crystallizing a third small-molecular organic material for forming the third small-molecular organic layer
Implementation Method 4
a glass transition temperature of a second small-molecular organic material for forming the second small-molecular organic layer is greater than a glass transition temperature of the third small-molecular organic material for forming the third small-molecular organic layer
Implementation Method 5
Organic Light Emitting Diode (OLED) is an organic thin film electroluminescence device
Data Source
AI summary
An OLED and a fabrication method thereof, and a display apparatus are provided. The OLED comprises: a base substrate; a first electrode, an organic functional layer and a transparent or semi-transparent second electrode sequentially disposed on the base substrate; and a covering layer provided on a side of the second electrode away from the base substrate. A surface of the covering layer away from the base substrate is uneven.